Push to connect (PTC) or push-in type fittings are used to connect a section of either plastic or metal tubing in a variety of fluid conveyance applications, such as in hydraulic or pneumatic systems. For example, in automotive applications, PTC fittings are used to connect sections of tubing in various systems of the automobile, such as in the cooling, braking, and fuel systems.
Conventional PTC fittings include a body portion having a bore therethrough and a tubular collet that is partially disposed within the bore of the body portion. An engaging structure, or gripper, is formed on the inner periphery of the collet. When the tubing is inserted into the collet, the gripper engages the tubing to prevent withdrawal of the tubing from the collet, and the tubing widens the portion of the collet that is disposed within the bore of the body portion, preventing removal of the collet from the body portion. To prevent leaking, an o-ring is provided within the bore of the body portion, inward of the collet, for engagement with the exterior surface of the tubing.
It is known to use grippers having a substantially triangular machined tooth. However, these types of grippers present a number of challenges. For instance, it is difficult to machine such a tooth accurately and consistently. Generally, a recess tool is used to machine the tooth, making the process time lengthy and expensive. Furthermore, since the tooth must be very sharp to retain the tubing within the fitting, there is a chance that the tubing can be scratched during insertion, preventing the o-ring from properly sealing with respect to the tubing.
Another known gripper uses tapped threads instead of a machined tooth. Since each turn of the thread effectively provides an additional engaging element along the longitudinal dimension of the tubing, the grip is increased, and thus, the threads need not be as sharp as the machined teeth. However, the required tolerances of such threads are tight. Thus, the threads are difficult to form accurately, and expensive tooling is required to form the tapped threads correctly. Furthermore, the tapping process may leave debris within the assembled fitting, which can prevent the o-ring from properly sealing with respect to the tubing.